I am looking at a 2005 T2000 on Ebay, but am confused by the listed size of
52/46. This seems to be inconsistent w/Trek tandem sizing of 54/44, 56/45, etc.
Checking online, I did find some dealer sites for 2005 that did indeed show the
52/46 size, but other sites confirm the more normal sizing. Can anyone explain the
apparent anomaly or are there really two different sizing conventions in play
(seems unlikely). Thanks!

Small is typically referred to as 54/44, even though the seat tube measures only 53cm. The 54cm number is the "virtual" seat tube height.

As to the apparent anomaly... You'll note that as you look at various different bike shops all of the Web sites look very much the same, right down to the pull down and pop-up menus, and even some of the broken links. That's because many shops are using the same 3rd party Web providers and, as such, they all end up with the same information on bikes, on-line special order parts catalogs, etc... with just enough customization -- bike shop logos and local information sections -- to make it look like an organic Web site. My "guess" as to why some Web sites show the 52/46 is that whoever was hosting the information used by the various bike shops punched in the wrong numbers for the Trek.

The '05 T2000 comes in 3 sizes (58, 56, 54), with the stoker sizing of (46, 45, 44). We ride a large. If you are looking on ebay, just have the seller take some measurements off the bike to make sure you are getting what you want.

It also looks like Trek altered the sizing a little for '07 (54, 56.5, 59).

I have a 2004 Trek T2000 for sale! In addition to standard components it has Campy Chorus shifters, dual computers and rear racl. Excellent condition both cosmetically and mechanically with 1500 miles.
$2150
Indianacbike@verizon.net

It also looks like Trek altered the sizing a little for '07 (54, 56.5, 59).

That may well be. Last time I talked with my "contact" at Trek he indicated they made some changes to the frame, e.g., update to the rear disc mount, new carbon fork with less rake (increases steering trail) and some "other" changes. The size of the frames may well have been another.

I have a 2004 Trek T2000 for sale! In addition to standard components it has Campy Chorus shifters, dual computers and rear racl. Excellent condition both cosmetically and mechanically with 1500 miles.
$2150
Indianacbike@verizon.net